"Global wildlife populations are set to have fallen by more than two thirds on 1970 levels by the end of the decade, conservationists warn.

Assessment of 14,152 populations of 3,706 species of mammals, birds, fish, amphibians, and reptiles from around the world reveals a 58 percent fall between 1970 and 2012 - with no sign the average 2 percent drop in numbers each year will slow.

By 2020, populations of vertebrate species could have fallen by 67 percent over a 50-year period unless action is taken to reverse the damaging impacts of human activity, the Living planet report from WWF and the Zoological Society of London (ZSL) said.  The figures prompted experts to warn nature was facing a global "mass extinction" for the first time since the demise of the dinosaurs.

African elephants in Tanzania have seen numbers crash due to poaching, maned wolves in Brazil are threatened by grasslands being turned into farmland and European eels have declined due to disease, over-fishing, and changes to their river habitats.

But add them together the WWF has.  It calls the cumulative measure the "living planet index," or LPI, which the report compares "the stock market index, except that, instead of monitoring the global economy, the LPI is an important indicator of the planet's ecological condition...based on scientific data from 14,152 monitored population of 3,706 vertebrate species (mammals, birds, fishes, amphibians, reptiles) from around the world."

And Colby Loucks, WWF deputy leader for wildlife and one of the people involved in the report, says there is a reason for condensing all the data to a single number.  "It's easier for media to grab onto it", he says.  "But," he says, the 58 percent number "does mask some interesting findings."  For example, that some animals living in freshwater are struggling far more than those living on land or in the oceans.  And that many individual species are increasing in population.

As for what the report does or doesn't tell us about the future of wildlife on our planet, the WWF index says the world is on track for global wildlife populations to have declined by two-thirds between 1970 and 2020.  Pimm points out that if this trend continued, there will be no wild animals at all on Earth by the middle of this century."

New Scientist Staff and Press Association Report 10/27/16